First, make a back up of everything, i just downloaded the whole /forum/ directory onto my hard drive...
The PM hack is the biggest hack out there, but only takes about 30 - 45 min to do, use something like cuteHTML where you can search for the text you need to replace.
Read twice, edit once. Its quite easy, and very well documented. I waited untill 3am to hack my board where if i made a big mistake, it would only be down for a few min, and nobody would be there to see it
Good luck!